You could write an custom form-decorator that uses a custom view-helper that only renders the open form tag. But I think this would be overkill.
Just "hardcode" the form-tags and fill the attributes with the data provided by the form-variable in your view.
<!--in your view-template -->
<form action="<?php echo $this->form->getAction() ?>"
enctype="<?php echo $this->form->getEnctype() ?>"
method="<?php echo $this->form->getMethod() ?>"
id="<?php echo $this->form->getId() ?>"
class="<?php echo $this->form->getAttrib('class') ?>" >
<!--in case your products are represented as elements -->
<?php foreach ($this->form->getElements() as $element): ?>
<?php echo $element ?>
<?php endforeach; ?>
<!--in case your products are represented as displayGroups -->
<?php foreach ($this->form->getDisplayGroups() as $displayGroup): ?>
<?php echo $displayGroup ?>
<?php endforeach; ?>
<!--in case your products are represented as subforms -->
<?php foreach ($this->form->getSubforms() as $subform): ?>
<?php echo $subform ?>
<?php endforeach; ?>
<!--in case your products are rendered by a view helper -->
<?php foreach ($this->products as $product): ?>
<?php echo $this->renderProduct($product) ?>
<?php endforeach; ?>
</form>
Just for fun the overkill way
// Get your products form
$form = new Form_Products();
// Add custom prefix path
$form->addPrefixPath('Foobar_Form_Decorator', 'Foobar/Form/Decorator', 'decorator');
// Set OnlyOpenTagForm-ViewHelper for FormDecorator
$form->getDecorator('Form')->setHelper('OnlyOpenTagForm');
// copy Zend/View/Helper/Form to Foobar/Form/Decorato/OnlyOpenTagForm.php
// In OnlyOpenTagForm.php
// replace Zend_View_Helper_Form with Foobar_View_Helper_OnlyOpenTagForm
// replace method "form" with onlyOpenTagForm"
// replace
if (false !== $content) {
$xhtml .= $content
. '</form>';
}
// with:
if (false !== $content) {
$xhtml .= $content;
}
Done! - The Java-Guys will love it ;)